This invention relates to rotors for large, high-capacity, internally ventilated electrical machines, in particular, such rotors which have a cooling air flow penetrating from both frontal sides into axial cooling channels of the rotor, e.g. cross ventilation, either by the fan action of the standard spacer webs in the individual radial cooling channels between the rotor lamination components and/or through open sections of the rotor winding or in some cases by a cooling air flow induced by separate frontally mounted fans.
Typically in such a rotor the axial cooling channels can be formed by openings spaced concentrically around the rotor shaft in the yoke area of the axially subdivided rotor laminations, or through the axial interspaces of a webbed shaft for the rotor laminations.
In a standard rotor having lamination components, arranged equidistantly with radial cooling channels of the same cross section positioned at equal intervals, there is an uneven air distribution from the frontal sides of the rotor to the rotor center, which depends upon the ratio of the axial channel to the radial channel cross section as shown by F. Wressing (dissertation, Berlin Technical University, 1972, "Ventilation Effect, Air Distribution and Ventilation Losses in Normal Axially Slotted Rotors for Large Electrical Machines"). According to that study, in the individual axial cooling channels the flow velocity in a symmetrically ventilated rotor begins initially slowly from the frontal sides to the rotor center and then increases markedly towards the rotor center such that the mid-sections are subjected to a much greater cooling action than the edge areas of the rotor. This means in the standard rotor design that, while some of the end sections of the rotor are getting the minimum required cooling, the mid-sections are receiving excessive cooling air distribution. This means the standard rotor expends more fan energy than necessary, cooling the mid-sections of the rotor; thereby, reducing overall efficiency.
The standard rotor lamination components design is also inflexible in that there is no provision for a case where the inflow conditions at one frontal side is different than the inflow at the other frontal side.
A modified rotor design having an uneven distribution of axial and radial cooling channels in such a manner that the cross sections would be smaller as they approached the rotor center in order to assure better cooling of the edge areas than of the inner area of the rotor would require varying stamped plates and varying spacers between the rotor lamination components, as well as a correspondingly more expensive assembly process. In addition, for manufacturing and operating reasons, the radial cooling channels cannot be made in the dimension required for this arrangement in widths below 6 to 8 mm, thus making this type of cooling distribution economically unattractive.
Accordingly, it will be appreciated that it would be highly desireable to provide rotor lamination components that had more even cooling air flow distributions which used equidistant spacings and evenly distributed channels, had ease of manufacturing, and yet has the flexility to adapt to unsymmetrical air flows.
It is an object of this invention to provide a more even distribution of the cooling air and a more constant cooling air volumetric flow overall, while reducing the fan losses in a design, using uniformly stamped rotor plates and uniform spacers, given an axially even arrangement of the rotor lamination components. It is another object of this invention to provide a more even distribution of the cooling air and a constant cooling air volumetric flow overall, while reducing fan losses, in a design using uniformly stamped rotor plates and uniformed spacers, given an axially even arrangement of the rotor lamination components even in the case of uneven frontal side cooling air inflow conditions.